Geology Reference
In-Depth Information
Table 2.17 Analyses of pseudobrookite from lamproites of different localities (after Wagner and
Velde (1986)
Al
2
O
3
FeO
t
a
Cr
2
O
3
MgO
MnO
TiO
2
Total
Fe
2
O
3
FeO
1
0.02
0.82
28.97
8.65
0.33
60.33
99.12
26.38
5.24
2
0.47
0.43
19.66
9.39
0.15
69.02
99.12
8.57
11.94
3
0.30
0.99
19.86
8.92
0.14
69.04
99.25
7.71
12.92
4
0.06
0.05
23.46
7.61
0.20
66.12
97.50
11.03
13.54
a
FeO
t
indicates total FeO + Fe
2
O
3
contents
1 Pseudobrookite from a Cancarix lamproites, Albacete Spain
2 Pseudobrookite from a Barqueros lamproite, Murcia, Spain
3 Pseudobrookite from a Smoky Butte lamproite, Montana, U.S.A.
4 Pseudobrookite from a Moon Canyon lamproite, Utah, U.S.A.
Around 40 % of this mineral is ferro-pseudobrookite (12
15 % pseudobrookite and
-
42
48 % karooite, Table
2.17
). In some of the lamproites from Murcia (Spain), the
pseudobrookite is very rich in MgO (up to 52 mol% karooite component), and it
resembles armalcolite.
-
2.19 Perovskite
Wade and Prider (1940) reported the presence of perovskite as an accessory mineral
in association with K-richterite in leucite-bearing rocks of West Kimberley. It is
present as a small dark reddish brown mineral with high relief. The pervoskites
from lamproitic rocks of Leucite Hills are enriched in Ce. Sr, Na and K. The
presence of high concentration of La
2
O
3
(2.03
2.05 wt%), Ce
2
O
3
(4.45
4.87 wt%),
-
-
Pr
2
O
3
(1.47
1.91 wt%) has been described by
Kuehner et al. (1981, for major element chemistry, see Table
2.18
).
In Prete della Scimmia, perovskite occurs as inclusions in green clinopyroxenes
contained within melilitite rocks. The low totals of the microprobe analyses may be
related to high REE contents. They show lower SrO (0.22
1.64 wt%) and Nd
2
O
3
(1.73
-
-
0.45 wt%) than that of
-
the co-existing apatites (1.2 wt%).
2.20 Ilmenite
In lamproites, ilmenite occurs as a common mineral after olivine, clinopyroxene
and phlogopite. They are poor in Fe
2
O
3
and constitute about 64
90 vol% FeTiO
3
-
component, 11
2 wt% pyrophannite. The lamproites from
Barqueros (Murcia, Spain) contain Mg-ilmenite with a rutile core.
30 % geikelite and 1
-
-
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